Viruses comprising the Flaviviridae family comprise at least three distinguishable genera including pestiviruses, flaviviruses, and hepaciviruses (Calisher, at al., J. Gen. Virol., 1993, 70, 37-43). While pestiviruses cause many economically important animal diseases such as bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV, hog cholera) and border disease of sheep (BDV), their importance in human disease is less well characterized (Moennig, V., et al., Adv. Vir. Res. 1992, 48, 53-98). Flaviviruses are responsible for important human diseases such as dengue fever and yellow fever, while hepaciviruses cause hepatitis C virus infections in humans. Other important viral infections caused by the Flaviviridae family include West Nile virus (WNV) Japanese encephalitis virus (JEV), tick-borne encephalitis virus, Junjin virus, Murray Valley encephalitis, St. Louis encephalitis, Omsk hemorrhagic fever virus and Zika virus. Combined, infections from the Flaviviridae virus family cause significant mortality, morbidity and economic losses throughout the world. Therefore, there is a need to develop effective treatments for Flaviviridae virus infections.
One common member of the Flaviviridae family is hepatitis C virus (HCV). HCV is the leading cause of chronic liver disease worldwide (Boyer, N. et al. J Hepatol. 32:98-112, 2000) so a significant focus of current antiviral research is directed toward the development of improved methods of treatment of chronic HCV infections in humans (Di Besceglie, A. M. and Bacon, B. R., Scientific American, October: 80-85, (1999); Gordon, C. P., et al., J. Med. Chem. 2005, 48, 1-20; Maradpour, D.; et al., Nat. Rev. Micro. 2007, 5(6), 453-463). A number of HCV treatments are reviewed by Bymock et al. in Antiviral Chemistry & Chemotherapy, 11:2; 79-95 (2000).
RNA-dependent RNA polymerase (RdRp) is one of the best-studied targets for the development of novel HCV therapeutic agents. The NS5B polymerase is a target for inhibitors in early human clinical trials (Sommadossi, J., WO 01/90121 A2, US 2004/0006002 A1). These enzymes have been extensively characterized at the biochemical and structural level, with screening assays for identifying selective inhibitors (De Clercq, E. (2001) J. Pharmacol. Exp. Ther. 297:1-10; De Clercq, E. (2001) J. Clin. Virol. 22:73-89). Biochemical targets such as NS5B are important in developing HCV therapies since HCV does not replicate in the laboratory and there are difficulties in developing cell-based assays and preclinical animal systems.
Currently, there are primarily two antiviral compounds, ribavirin, a nucleoside analog, and interferon-alpha (α) (IFN), that are used for the treatment of chronic HCV infections in humans. Ribavirin alone is not effective in reducing viral RNA levels, has significant toxicity, and is known to induce anemia. The combination of IFN and ribavirin has been reported to be effective in the management of chronic hepatitis C (Scott, L. J., et al. Drugs 2002, 62, 507-556), but less than half the patients given this treatment show a persistent benefit. Other patent applications disclosing the use of nucleoside analogs to treat hepatitis C virus include WO 01/32153, WO 01/60315, WO 02/057425, WO 02/057287, WO 02/032920, WO 02/18404, WO 04/046331, WO2008/089105 and WO2008/141079, but additional treatments for HCV infections have not yet become available for patients.
Virologic cures of patients with chronic HCV infection are difficult to achieve because of the prodigious amount of daily virus production in chronically infected patients and the high spontaneous mutability of HCV virus (Neumann, et al., Science 1998, 282, 103-7; Fukimoto, et al., Hepatology, 1996, 24, 1351-4; Domingo, et al., Gene, 1985, 40, 1-8; Martell, et al., J. Virol. 1992, 66, 3225-9. Experimental anti-viral nucleoside analogs have been shown to induce viable mutations in the HCV virus both in vivo and in vitro (Migliaccio, et al., J. Biol. Chem. 2003, 926; Carroll, et al., Antimicrobial Agents Chemotherapy 2009, 926; Brown, A. B., Expert Opin. Investig. Drugs 2009, 18, 709-725). Therefore, drugs having improved antiviral properties, particularly enhanced activity against resistant strains of virus, improved oral bioavailability, fewer undesirable side effects and extended effective half-life in vivo (De Francesco, R. et al. (2003) Antiviral Research 58:1-16) are urgently needed.
Anti HCV 2′-deoxy-2′-fluoro-nucleosides and nucleotides have been disclosed by Sofia (WO/2008/121634), Attenni (WO/2008/142055), Narjes (WO/2008/085508), Wang (WO/2006/012440), Clark (WO/2005/003147) and Sommadossi (WO/2004/002999) but none of these compounds have become available for patients.
Influenza viruses of the Orthomyxoviridae family that belong to the genera A and B are responsible for seasonal flu epidemics each year, which cause acute contagious respiratory infections. Children, the old, and people with chronic diseases are at high risk to develop severe complications that lead to high morbidity and mortality rates (Memoli et al., Drug Discovery Today 2008, 13, 590-595). Among the three influenza genera, type A viruses are the most virulent human pathogens that cause the most severe disease, can be transmitted to other species, and give rise to human influenza pandemics. The recent human influenza outbreak of the aggressive porcine A/H1N1 strain in 2009 has emphasized the need for novel antiviral therapeutics. While yearly vaccination programs are currently used to protect populations from influenza infection, these programs must anticipate the virus strains that will be prevalent during seasonal outbreaks to be effective and they do not address the problem of sudden, unanticipated influenza pandemics. The recent human influenza outbreak of the aggressive porcine A/H1N1 strain in 2009 is an example of this problem. Therefore there is a continuing need for novel anti-influenza therapeutics.